The present invention is a gyro platform assembly that is on a spinning vehicle, such as a spinning space vehicle. The vehicle holds the gyro platform assembly. The assembly has a frame. The frame holds a torquer motor and resolver. The torquer motor and resolver hold a gimbal. The gimbal rotatably holds a platform. The rotation axis of the gimbal is made to be aligned along the spin axis of the spinning vehicle. The rotational axis of the platform is perpendicular to the rotational axis of the gimbal.
The assembly has three rate gyros. The three rate gyros are on the platform. The three rate gyros have mutually orthogonal input axes.
The gimbal can be maintained in a chosen, space-fixed, orientation by counter-rotating the gimbal within the spinning vehicle and with respect to the angular direction of spin of the spinning vehicle. The gimbal is counter-rotated at an angular rate that is equal in magnitude to the angular rate of the spinning vehicle. The gimbal can be rotated by means of a torquer. The counter-rotational angular direction of the gimbal can be made to be opposite to the angular direction of spin of the vehicle.
A drift rate of a sensing axis of each rate gyro can be determined when there is no coning and the gimbal is counter-rotated within the spinning vehicle. The drift rate of each of the three sensing axis is equal to the output of that sensing axis. This is the case when the coning angle of the vehicle is zero.
If there is coning and counter-rotation is applied to the gimbal, the platform can be slowly carrouseled. By comparing differential position measurements, from opposite 180 degree orientations, for gyro input axes that are perpendicular to the carrousel axes, gyro bias in these input axes can be observed and significantly eliminated as an error source. Such gyro bias can be due to the effects of coning motion, misalignments and scale factor errors.
If there is coning and the gimbal is not counter-rotated, the platform can be slowly carrouseled. The outputs of the sensing axes that are perpendicular to the spin axis of the vehicle are averaged. The averaged output of each such perpendicular output axis is the drift rate of that axis.
If there is no coning and the gimbal is not counter-rotated, the outputs of the sensing axes that are perpendicular to the spin axis of the vehicle are equal to the drift rates of these axes.